#include<stdio.h>
int main() {
	float mu = 1.0;
	float zi = 2.0;
	int x;
	float sum = 0.0;
	float he=0.0;
	scanf_s("%d", &x);
	for (int i = 0; i < x; i++) {
		int temp;
		sum += zi / mu;
		he = zi + mu;
		temp = zi;
		zi = he;
		mu = temp;
	}printf("%f", sum);
}